How old is the cat?? My dog had a severe heart murmur as a pup and my vet told me he wouldn't live past two or three years old! I was heart broken as this is what she told me at his FIRST vet appointment. Luckily for me he has outgrown it and is doing great today at almost 4 years old. We also have elderly cats with heart murmurs and they have no symptoms as of yet. They are getting up there in age and if their heart starts to fail then we'll deal with it when it happens.